Circuit breaker operating mechanism



Oct. 20, 1953 J. K. HODNETTE ET A1.

CIRCUIT BREAKER OPERATING MEcHANIsM original F'iled July 5, 1947 2 Sheets-Sheet l BNN Oct. 20, 1953 J. K. HODNETTE ETAL CIRCUIT BREAKER OPERATING MECHANISM 2 Sheets-Sheet 2 Original Filed July 5, 1947 Patented Oct. 20, 1953 CIRCUIT BREAKER OPERATING MECHANISM John K. Hodnette, Pittsburgh, and Merrill G. Leonard, Sharon, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Original application July 5, 1947, Serial No.

759,272, now Patent No. 2,586,429, dated February 19, 1952. Divided A'and this application August 8, 1951, Serial No. 240,876

6 Claims. (Cl. ZOO-116) This invention relates to circuit breakers, and more particularly, to operating and tripping mechanism therefor.

This application is a division of copending ap-V plication Serial No. 759,272, filed July 5, 1947, by John K. Hodnette and Merrill G. Leonard, now Patent No. 2,586,429, issued February 19, 1952 and assigned to the assignee of the present invention.

One object of the invention is to provide a circuit breaker embodying an improved operating mechanism wherein the load of the main operating spring is not imposed on the breaker latch.

Another object of the invention is to provide a circuit breaker embodying a trip member controlled by a thermal trip element to trip the breaker and to effect an indication of the condition of the breaker, and an indicating trip member controlled by said thermal trip element to eiiect an indication of the approach of a dangerous circuit condition.

Another object of the invention is to provide a circuit breaker embodying a trip member controlled by a thermal trip element to trip the breaker and to effect an indication of the condition of the breaker, an indicating trip member controlled by said thermal trip element to effect an indication of the approach of a dangerous circuit condition and means operatively relating the operating mechanism of the breaker and the indicating trip member to permit resetting of said indicating trip member without disturbing the breaker Contact position.

Another object of the invention is to provide a circuit breaker embodying a thermal trip device responsive to overload current to trip the breaker and an auxiliary thermal element responsive to ambient temperatures to control the thermal trip device to trip the breaker after a relatively long time delay when the ambient temperature is low and after a relatively short time delay when the ambient temperature is high.

The novel features that are considered charq acteristic of the invention are set forth in parv ticular in the appended claims. The invention itself, however, both as to structure and operation, together with additional objects and advantages thereof, will best be understood from the following detailed description thereof when read in conjunction with the accompanying drawings.

In said drawings:

Figure 1 is an elevational sectional view taken along line L-I of Fig. 2 showing a circuit breaker embodying the principles of the invention, the breaker being shown in the closed position,

Fig. 2 is a sectional view taken o n line II.-II of Fig. 1 and looking in the direction of the arrows,

Fig, 3 is an elevational view similar to Fig. 1 but showing the breaker in the tripped open position, and

Fig. 4 is an elevational View similar to Fig. l but showing the parts in the reset position.

Referring to Fig. 1 of the drawings, the circuit breaker comprises a base II of insulating material on which is mounted the breaker contact structure, a metal housing I3 secured to the base II, an operating mechanism indicated generally at I5 and a trip device indicated generally at I1.

The contact structure comprises a main stationary contact I9 rigidly mounted on the inner end of a rod 2I slidably mounted in the base II. A coil spring 23 surrounds the rod 2l and is compressed between the base II and a connector 25 secured to the rod 2| and to the contact I9 to provide contact pressure. A limit nut 21 is threadedly mounted on the rod 2I outside the base II. A cooperating movable contact 29 is rigidly mounted on a channel-shaped switch arm 3| pivotally mounted cn a pivot pin 33 supported in a U-shaped bracket 35. The bracket 33 is secured to the base II by means of a screw 31.

The contact structure also comprises a stationary arcing contact 39 rigidly mounted on a conducting support member 4I secured by means of a screw 43 to the base II, and a cooperating movable arcing contact 45. The movable arcing contact 45 is rigidly mounted on a channel-shaped switch member 41 which straddles the switch arm 3| and is pivoted on the pivot pin 33. A com pression spring 49 disposed between an extension 5I of the main switch arm 3l and the yoke portion 53 of the arcing contact switch arm 41 provides contact pressure for the arcing contacts 39-46 and also maintains the arcing contacts in closed position until after the main contacts I9-29 have separated on an opening operation.

The operating mechanism I5 is supported in a generally U-shaped frame 55 the bight 51 of which is rigidly secured to the housing I3. The operating mechanism comprises a releasable member or carrier 59 pivotally mounted on a fixed pivot pin 6I mounted in the side members of the frame 55. The carrier 59 has a latch portion B3 adapted to engage a latch member 65 forming part of the trip mechanism which will be more fully described hereinafter. The carrier 59 is biased in a clockwise direction by means of a spring 61 which surrounds a spring guide 69 pivotally connected at one end by means of a U pivot pin 'il to the carrier. The spring 61 is compressed between a shoulder on the spring guide @3 and a rod 13 mounted on and extending between the side members of the frame 55. The carrier 59 is operatively connected to the switch arm 3| by means of a toggle comprising toggle links i3 and 11 pivotally connected together by a knee pivot pin 1Q. rIhe toggle link 15 is of insulating material and is pivotally connected to the witch arm 3| by means of a pivot pin 3|. The toggle link 11 is pivotally connected by means of a pivot pin S3 (Fig. 3) to the carrier 53. The pivot pin 83 is directly under and concentric with the pivot pin 39 (hereinafter described) when the carrier 59 is in its normal latohed position, as shown in Fig. 2. The pivot pin 8| projects beyond the side members of the switch arm 3| and through elongated slots S (only one being shown) in the side members of the arcing contact switch arm 41.

An actuator comprising a pair of spaced actuating levers 3? is provided for operating the toggle i5- l1 to manually open and close the contacts. The actuating levers S1 are disposed adjacent the inner sides of the U-shaped frame 55 and each of the levers carries a pivot pin 89 which is seated in a slot 9| in the adjacent frame. rihe actuating levers 81 are rigidly joined by an integral cross member 93 and each of the levers El is provided with a hook portion 35 which in the closed position of the mechanism engages an end of the knee pivot pin 19 to hold the toggle 'iS-11 in a slightly underset position to thereby hold the switch arms 3| and 41 in the closed contact position.

A pair of overcenter springs 91 is provided to operate the levers 81 and therethrough the toggle -11 in order to manually open and close the circuit breaker The springs 91 have one end hooked over laterally projecting ears 3S on the levers 81 and the other ends of the springs are hooked over an operating rod |9| extending through guide slots |33 disposed in parallel alignment in the frame members 55. Secured to a shaft |95 for rotation therewith is a pair of 0perating arms |61 each having its free end bifurcated to embrace the rod HH adjacent the ends thereof. The shaft |5 is pivotally supported in plates |39 secured to the outside of the housing i3 and provided with mounting feet l whereby the circuit breaker may be mounted on a suitable support (not shown). One end of the shaft |535 extends to the outside of the housing and has secured thereto an operating handle indicated at i3 (Fig. 2) for manually operating the shaft |95 and the arms m1.

The circuit breaker may be opened manually by rota-tingthe handle I I3 and consequently the shaft E35 and arms |01 approximately 90 in a counter-clockwise direction from `the position shown in Fig. l. During this movement the arms |31 cause the rod lil! to move upwardly in the slots 33 carrying therewith the ends of the springs 91 attached thereto. When the rod |25 moves the line of action of the springs |01 overcenter above the pivot 89 of the levers 81, they bias the actuator levers 81 in a clockwise direction. Continued movement of the arms |01 and the rod ||i| increases the biasing force until a point is reached when the springs rotate the actuating levers 81 clockwise about the pivots 89. In the closed and latched position of the circuit breaker, the pivot 83 connecting the toggle link 11 to the releasable carrier 59 is in axial alignment with the pivot 89 of the actuating lever 81 and the knee pivot pin 19 remains in engagement with the hook 95, consequently, the toggle link 11 and the lever 81 will move as a unit during manual opening operation. The clockwise movement of the actuator lever 81, therefore, causes collapse of the toggle 'i5-11 and opening of the contacts. During the opening movement of the mechanism the switch arm 3| is first moved in a counterclockwise or opening direction to open the main contacts |9-29 while the spring 49 maintains the arcing contacts 39-45 closed until after the main contacts have separated. Shortly after the main contacts have separated, the pin 8| engages the outer end of the slot 85 in the switch arm 41 and thereafter moves both switch arms 3|-41 to the full open position in unison in which position the parts are shown in Fig. 4.

The contacts are closed by rotating the shaft |05 and the arms |01 clockwise from the Fig. 4 position to the position in which they appear in Fig. 1. During this movement the arms |01 carry the rod ||l| therewith moving the line of action of the springs 31 over-center below the aligned pivots 83-89, whereupon the springs 91 bias the actuating lever S1 in a counterclockwise direction, and, since the knee pin 19 'of the toggle 15-11 is in engagement with the hook 95, the toggle is biased t0 its underset position. Continued clockwise movement of the arms |61 increases the spring bias on the actuating lever 81 and the toggle until a point is reached where the springs 91 suddenly straighten the toggle 15-11 and close the contact with a snap action.

The configuration of the slot |63 is substantially concentric with the ears 99 on the actuating levers 8l so the slot controls the springs 91 so as to produce as little change as possible in the length of the overcenter springs 91 until the toggle is broken, thereby reducing the energy required to operate the breaker. As will be more fully brought out later, the shape of the slots |03 also controls the operation of a reset lever.

The circuit breaker may be tripped open automatically by operation of the trip device I1 in response to overload currents. The trip device comprises a base ||5 of insulating material secured to the housing i3, a cover l |1 also of ine sulating material secured to the base ||5 by means of rivets ||9 (only one being shown), a biased member |2| releasable to actuate the latch 35 and a tripping bimetal element |23 which is operable to release the member 2| The bimetal element is secured at one end to a metal bracket |24 supported on insulating plate |25 mounted on the base ||5 and at the other end carries an insulating block |21 to which is secured a metal latch |29. A connector |3| is electrically connected to the free end of the bimetal element and a flexible terminal conductor |33 is connected to the connector. The flexible conductor |33 extends to the left and is supported on a bracket |35 mounted on the base H5. Thereafter the conductor |33 extends out through an opening in the cover ||1 where it serves to connect the breaker in an electrical circuit. The bracket |24, and hence, the xed end of the bimetal element is connected by means of a flexible conductor |31 to the switch arms 3| and 41, the conductor |31 extending downwardly through an opening in the base ||5 where it is mechanically and electrically secured to a connector I 39, and to the switch arms 3| and 41. rfhe connector |39 provides a point where a terminal strip |46 may be connected to provide a third terminal between the bimetal and the controls. The main stationary contact I9 is connected by means of a flexible conductor I4I to the stationary arcing contact 39 and the circuit through the breaker is completed by means of a flexible terminal conductor I 43 also connected to the fixed arcing contact 39 and extending out through an opening in the base II. An auxiliary bimetal element M5, disposed above the tripping bimetal |23 but insulated therefrom by a strip |41 of insulating material, is fixedly mounted at its left-hand end and adapted to deflect, when heated, in the same direction as the tripping bimetal |23.

The releasable member |2| is pivotally mounted at |49 on an adjusting arm |5| which, in turn, is pivotally mounted on a pivot pin |53 which is supported in a suitable opening in the base I l5. The pivot |49, adjusting cam I5I and pivot pin |53 are directly behind pivot |89, a second adjusting cam I9I, and pivot pin |43, as hereinafter described. The member |2| is biased by means of a spring |55 in a clockwise or tripping direc-tion. The spring |55 has one end hooked into an opening in the member |2| and the other end anchored to the free end of the adjusting arms |5|. Secured to the adjusting arm |5| at a point adjacent its free end is a rod |51 (Fig. 2) which extends upwardly through an enlarged opening in the base ||5 and has its upper end threaded to receive an adjusting nut |59. A spring |6| coiled about the rod |51 and compressed between the bottom surface of the base I|5 and a washer |63 biases the free end of the arm |5I downwardly. By turning the nut |59 in one direction the rod |51 may be moved upwardly rotating the arm |5| in a counterclockwise direction. Turning the nut |59 in the opposite direction permits the spring |6| to lower the rod |51 and rotate the arm |5| in a clockwise direction. Since the releasable member |2| is pivotally supported at |49 on the arm |5|, it will be thus moved up or down relative to the latch |29 to thereby vary the overlap of the member |2| with the latch.

The latch member 65 is U-shaped and the two legs thereof are mounted on a shaft |65 for movement therewith, the shaft |65 being mounted for rotation in openings in the side members of the frame 55. The yoke portion |61 of the latch member is shaped inwardly to form a latch portion |69 which engages the latch portion 63 of the carrier 59 to normally restrain the latter in the position shown in Fig. 1.

The bimetal element |23 has its high-expansion. side facing downwardly so that, when heated a predetermined amount in response to overload currents, the bimetal element |23 will deflect upwardly to disengage the latch |29 from the releasable member |2I. When this occurs, the spring |55 rotates the member |2| clockwise about its pivot |49 and the lower end |1| thereof strikes the latch member 65 a blow to disen gage the latch portion |69 thereof from the latch portion 63 of the carrier 59 thereby releasing the carrier. Upon release of the carrier 59, the spring 91 rotates the carrier in a clockwise direction about its pivot 6| to the position in which it appears in Fig. 3, thus moving the switch members 3| and 41 to the open position. During the early portion of this movement the knee pin 19 of the toggle "G5-19 moves out of the hook portion 95 of the actuator levers 81 and shortly thereafter' the end of the spring guide 69 strikes the toggle link 11. This action causes collapse of the toggle and rotates the toggle link 11 clockwise about its pivot 83 to effect movement of the switch arms 6 3|-41 to the open position. The mechanism is shown in Fig. 3 in the tripped open position.

During the automatic opening operation, the knee pivot pin 19, as previously set forth, escapes from the actuating levers 81 and before the breaker can be reclosed it is necessary to reengage the actuating levers with the knee pin 19 and also to reset and relatch the carrier 59. Both of these operations are accomplished by moving the rod IBI upwardly in the slots |93 from the Fig. 3 position to the position shown in Fig. 4. This is done by rotating the shaft |95 and the arms |91 in a counterclockwise direction as far as they will go, the movement of the rod being limited by engagement with the upper end of the slot |03. During this movement the rod ||l| carries the line of action of the springs 91 overcenter above the pivot 99 (Fig. 3) of the levers 81 whereupon the springs 91 actuate the levers in a clockwise direction until they engage the knee pin 19. Next in its upward travel, the rod IUI engages a projection |13 on the carrier 59 and rotates the carrier counterclockwise about its pivot 5|. Near the end of this movement of the carrier 59 the latching end thereof wipes by the latch portion |69 of the latch member 65 which is then restored clockwise to latching position by means of a spring |15, the clockwise movement of the latch 65 being limited by engagement with the frame 55. During the counterclockwise movement of the carrier 59, the pivot 83 for the toggle link 11 moves back slightly beyond the normal position in which it is aligned with the pivot 89 of the levers 81. This movement thrusts the knee pin 19 into the hook portion of the levers 81, and provides a slight overthrow for the latching portion 63 of the carrier beyond latched position.

The rod IDI in its upward travel, next engages a cam surface |11 in one wall of a slot |19 in a resetting lever |8| which is pivotally mounted on the pivot pin 6|, and in cooperation with the slots |03, moves this lever counterclockwise about its pivot. During this movement, an ear |93 (Figs. 2 and 4) formed at right angles to the upper end of the resetting lever engages the releasable tripping member |2| and rotates it counterclockwise past its latched position as shown in Fig. 4. The parts are now in the reset position as shown in Fig. 4, in readinessJ for a contact closing operation which is effected in the previously described manner by movement of the arms |91 and the rod |0| in a clockwise direction to the Fig. 1 position, during which movement the actuating levers 81 acting through the knee pin 19 straightens the toggle 'E5- 11 and moves the switch arms to their closed positions. As the rod |9| nears the lower end of its movement, it engages a portion of the slot |19 in the resetting lever |8I and restores this lever to its initial position, as shown in Fig. l.

The circuit breaker is designed for use in an oil insulated transformer, and it is the purpose of the auxiliary bimetal element |55 to modify the tripping time of the current-carrying tripping bimetal element |23 in accordance with the temperature of the surrounding medium. The bimetal element |45 is similar to the tripping bimetal |23 and also has its high-expansion side facing downwardly, hence, when heated, will deiiect in the same direction as the tripping blmetal 23.

If the transformer temperature rises gradually so that the mass of copper, oil insulation, etc., tend to reach their maximum safe temperatures, the auxiliary bimetal ill, which is heated by the oil temperature rise and to some extent by conduction and convection from the tripping bimetal |23, will deflect in the same direction and at approximately the same rate as the tripping bimetal |23 which is heated by both current l'iow and oil temperature rise, hence the bimetal |125 will not appreciably change the trip-time curve of the tripping bimetal |23. if the transformer temperature is low and a heavy overload occurs, the tripping bimetal iis will be heated rapidly, whereas the temperature of the auxiliary bimetal |55 will rise very little and will, therefore, exert a restraining force on the tripping bimetal I .lt will be seen, therefore, that for a given value of overload current, the circuit breaker will be tripped open after a relatively short time delay when the transformer temperature is high and after a relatively long time delay when the transformer temperature is low. By use of the auxiliary bimetal heavier overloads may be carried for a short time without tripping, and the greater temperature rise required to trip on such overloads will give faster cooling and thereby the time for resetting is reduced.

The trip-time curve of the trip device may be varied by substituting bimetal elements having different characteristics for the auxiliary bimetal element, by varying the space between the tripping bimetal and the auxiliary bimetal and by varying the thermal insulation between a-nd around the bimetal elements and also by varying the characteristics o the tripping bimetal.

Means is provided for indicating a partial overload condition which is not of sufficient magnitude to trip the breaker open but which indicates that the current in the circuit is approaching a dangerous overload condition or that a dangerous overload condition has been approached and then cleared itself without tripping the breaker, also to indicate that the breaker has been tripped open in response to a dangerous overload condition.

The indicating mechanism comprises a releasable member |81 (Figs. 1 and 2) pivotally sup- L.

ported by means of a pivot pin ISB or an adjusting lever I9|. The lever Il is pivotally mounted on the pivot pin i133 which supports the lever i 5i on the base IIE of the trip device. A spring |95 having one end hooked in an opening in one arm of the releasable member |81 and the other end hooked in an opening in the lever ISI biases the member |81 in a clockwise direction about its pivot his. rPhe member |81 is normally restrained against clockwise movement by engagement with the latch |29. An adjusting rod |91 (Fig. l), similar to the rod |51 (Fig. 2) for the lever |5I, is secured to the lever I9! at a point near its free end and extends upwardly through an opening in the base IIS. The upper end of the rod i9?" is threaded to receive an adjusting nut |98 and a compression spring Zi coiled about the rod i S1 is disposed between the base I I5 and a washer 263 bearing against the lever ISI. By this means the lever IS! can be moved up and down about its pivot |533 to thereby shift the pivot 89 for the member 31 and vary the amount of overlap between the member |81 and the latch |29. The member |81 is adjusted to be released by the latch i251 before the bimetal element |23 deflects far enough to release the member l2| to trip the breaker. The releasable member |81 is electrically connected by means of a flexible conductor 2%5 to a conductor 231 extending transversely through the breaker and secured to the base I|5 of the trip device. The member |81 is made of conducting material and carries a stud or contact 269 also of conducting material which, upon release and clockwise movement of the member |81 is adapted to make butt engagement with the end of a xed contact 2|| to thereby close an electrical circuit and energize an indication device (not shown) but preferably a signal light to give visual indication.

The releasable trip member I 2| is also electrically connected by means of a flexible conductor 2 I3 to the conductor 201 and carries a contact 2I5 which, upon release of the member to effect tripping of the breaker, engages the end of a,

fixed contact 2|1 directly behind the xed contact 2|I and closes an electrical circuit to energize an indicating device. The xed contacts 2 I and 2 I 1 may be connected together and connected in a circuit (not shown) to energize a single indicator or they may be connected in separate circuits to energize separate indicators. The return circuit (not shown) from the indicators is connected to a supply conductor 2|9 also secured to the base ||5 but insulated from the supply circuit 201. The supply conductors 201 and 2 I9 extend outside of the housing I3 (Fig. 2) to be connected to a supply circuit, or to be connected to similar conductors in another circuit breaker assembled adjacent to the rst breaker in a manner to be more fully described later.

As previously stated, the releasable signal member I 81 is adjusted by means of the lever |9I and the adjusting rod |91 (Figs. 1 and 2) to trip and close the circuit to the indicator before the releasable trip member |2I is released to trip the breaker. Hence, if an overload current occurs which approaches a dangerous value and trips the signal member |81, but which is cleared before it releases the trip member 12|, the member |81 will close its circuit and energize the indieating means. Under this circumstance, it is desirable to reset the member |81 without opening or otherwise disturbing the main breaker contacts. This is accomplished by a partial stroke of the arms |01 and the rod I DI in opening direction which is elected by a partial opening stroke of the handle |I3 (Fig. 2). During this partial stroke, the rod ISI engages the cam portion |85V of the resetting member I8I and rotates this member in a clockwise direction from its Fig. 1 position causing an ear 22| on the member I8| to engage an arm 223 on the member |31 to rock the latter in a counterclockwise or resetting direction to its relatched position as shown in Fig. 1. After the release signal member |81 is relatched, the arms |61 and the rod lei are restored clockwise to their normal positions and since the rod IBI was not moved far enough to carry the springs 91 overcenter, the main contacts remain in their closed position. If a single indicating device is utilized which is energized by both the releasable member |2| and |31 with their contacts electrically connected in parallel, and this indicator remains energized after the member |81 has been reset, it indicates that the breaker has been tripped open and must be reset and reclosed. However, with two indicators operated independently by the member |81 and the trip member l2 I, a single energized indicator would inform the attendant that an overload had occurred but had cleared without tripping the breaker, in which event it would only be necessary to reset the member |81 without opening the breaker. If both indicators were energized the attendant would know immediately the breaker was tripped open and must be reset and then reclosed.

As previously stated, two or more circuit breakers may be assembled and tied together for unitary operation to control a multi-phase circuit. While only a single circuit breaker has been described, the breakers to be assembled are identical, hence, only the means for providing unitary operation of two or more circuit breakers will be described. When two or more breakers are assembled together, the .plates |08 together with the mounting feet are omitted except those on the outside of the end `c-reakers and the breakers are secured together by means of a plurality of bolts 225 (Figs. i and 2) passing through all of the assembled breakers and having nuts 221 threadedly engaging the ends thereof. The trip shafts |85 and the latch members 65 are tied together for unitary movement by means of a sleeve 22s (Fig. 2) which couples the shafts |65 so that a tripping operation of the latch member' 65 for one oi the breakers in response to an overload current occurring in the related phase circuit will operate the latch members for all of the breakers. The operating shaft |85 described for the single pole breaker is replaced by a similar shaft 23| (Fig. 2) which extends through all oi the breakers and has secured thereto for movement therewith the operating arms |51 for each breaker. Operation of the shaft 23| will effect manual opening and closing of the contacts of all of the breakers, reset and relatch the mechanism and reclose the contacts of all the breakers in the same manner as was described for the single pole unit.

The supply conductor 201 for the indicator device of each phase breaker is provided at one end with a spring clip 233 (Fig. 2) for releasably receiving the externally projecting end of the conductor of the adjacent phase breaker so that the supply circuit extends through all of the breakers. The supply conductors 2|9 .are grounded to their respective metallic housings.

From the foregoing description, it will be apparent that there is provided a circuit breaker embodying a tripping mechanism controlled by a thermally responsive element for opening the breaker contacts under certain overload current or temperature conditions and for effecting an indication of the condition of the breaker operating mechanism. There is also provided a second trip mechanism controlled by the thermally responsive element for effecting an indication of the approach of a dangerous overload or temperature condition of a lesser magnitude than that required to trip the breaker. The arrangement of the trip mechanisms being such that in the event the condition which caused operation of the second trip mechanism disappears without having tripped the breaker, the trip mechanism may be reset by partial operation of the breaker operating mechanism without disturbing the position of the breaker contacts. There is also provided independent adjusting means for adjusting the trip mechanism to vary the amount of overload current required to trip the breaker and for independently adjusting indicating trip mechanism to vary the amount of overload and/or temperature rise required to effect an indication without tripping the breaker.

Having described the invention in accordance with the patent statutes, it is to be understood that various changes and modifications may be made in the structural details thereof without departing from some of the essential features of the invention.

We claim as our invention:

1. In a circuit breaker comprising a member releasable to effect automatic opening of said breaker, a trip device comprising a tripping bimetal element connected in the circuit controlled by the breaker to be heated in response to overload currents, said bimetal element when heated a predetermined amount dei'lecting to release said releasable member, and a second bimetal having its high-expansion side disposed closely adjacent to but insulated from said tripping bimetal element to be heated by the surrounding medium, said second bimetal element normally opposing tripping deiiection of said tripping bimetal element when said tripping bimetal deects in response to heating thereof, and said second bimetal element when heated defieoting away from said tripping bimetal.

2. In a circuit breaker comprising a member releasabie to effect opening of said breaker, a trip device comprising a first bimetal element xedly mounted at one end and capable of dcfiection when heated to release said releasable member., means connecting said bimetal element in the circuit to be heated in response to overload currents therein, and a second bimetal element disposed immediately adjacent said first bimetal element but insulated therefrom, said second bimetal element normally opposing deflection of said first bimetal element when said first bimetal element deflects in response to heating thereof, said second bimetal defiecting solely by heat transmitted thereto from the surrounding medium, and the second bimetal when so heated delecting away from said rst bimetal element to permit free deflection of said first bimetal element.

3. In a circuit breaker comprising a member releasable to effect automatic opening of said breaker, a first bimetal element disposed to be heated by the current of the circuit and when heated a predetermined amount deecting in a direction to release said releasable member and a second bimetal element having its high-expansion side disposed immediately adjacent the low-expansion side of said iirst bimetal element to normally oppose deflection of said rst bimetal element in response to heating thereof with a predetermined force, said second bimetal element being heated by heat transmitted thereto from the surrounding medium and when heated deflecting in the same direction as the first bimetal element to decrease the opposing force in accordance with the amount of heating of said second bimetal element.

4. In a circuit breaker having a member releasable to effect automatic opening or said breaker, a rst bimetal element releasably restraining said releasable member, said rst bimetal element being disposed to be heated by the current of the circuit and when heated a predetermined amount deiiecting in a direction to release said releasable member, a second bimetal element disposed parallel to and immediately adjacent to said first bimetal element and insulated therefrom, said second bimetal element when cold opposing deiiection of said rst bimetal element in releasing direction with a predetermined force, and said second bimetal element being heated by the surrounding medium and when heated deflecting away from said rst bimetal element to reduce the opposing force according to the rise in temperature of the surrounding medium.

5. In a circuit breaker having a member releasable to eeot opening of said breaker, a rst bimetal element supported at one end and having the other end free, said free end of said iirst bimetal element normally engaging and releasably restraining said releasable member, said first bimetal element being heated by the current of the circuit and when heated a predetermined amount bending in a direction to disengage the free end thereof from said releasable member, a second bimetal element having one end supported adjacent the supported end of said rst bimetal element and having the high-expansion side thereof extending along the low-expansion side of said ist bimetal element but insulated therefrom to normally oppose thermal bending of said rst bimetal element, and said second bimetal element being heated by heat transmitted thereto from the surrounding medium and when heated bending in the same direction as said iirst bimetal element thereby decreasing the force with which it opposes thermal bending of said iirst bimetal element.

6. In a circuit breaker comprising means releasable to eiTect opening' of said breaker, a

tripping bimetal element heated by the current of the circuit, latch means on said tripping bimetal element engaging and releasably restraining said vreleasable means, thermal bending of said tripping bimetal element when heated in response to overload currents in said circuit causing said latch to release said releasable means, an auxiliary bimetal element having its highexpansion side extending along the low-expansion side of said tripping bimetal but insulated from said tripping bimetal element and normally opposing thermal bending of said tripping bimetal element, said auxiliary bimetal element being heated by heat transmitted thereto from the surrounding medium and when heated in response to a rise in temperature of said surrounding medium bending in the same direction as the thermal bending of said tripping bimetal element to permit the latter to release said releasable means quicker when the surrounding medium is hot than when it is cold.

JOHN K. HODNETTE. MERRILL G. LEONARD.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,210,262 Sachs Aug. 6, 1940 2,318,279 Aschvvanden May 4, 1943 2,411,351 Armstrong Nov. 19, 1946 

